Support is often required for loads bearing onto surfaces over areas where closure of the load bearing surface onto the underlying base has to be prevented or controlled. This is the case in underground mining, and in emergency and rescue operations conducted in earth quake zones where structures such as buildings, bridges and some geological formations become unstable, and have to be supported at least temporarily to allow for such operations to be safely conducted. Supports are also required permanently in the case of underground mine supports.
A problem in such situations is that often a load may shift and may further endanger the lives of people trapped in such areas, or emergency and rescue personnel attending to such scenes. In the mining industry the occurrence of such situations are not emergencies but is the result of the mining operations. However, if not handled properly it can lead to enormous danger and loss of life.
In particular, during underground mining operations huge volumes of rock are removed which leaves equivalent sized open spaces that need to be supported to prevent sudden and unexpected closure of such spaces by surrounding rock.
The space created by the removal of rock is bounded by a hanging wall, which is the “roof” of the space, and a foot wall, which is the “floor” of the space. Supports are used to keep the hanging wall and foot wall apart. These supports typically include temporary supports, short term supports and permanent supports.
Temporary supports include extendable metal supports which are used between the hanging wall and foot wall immediately in front of the working face. The temporary supports are installed as soon as possible after an area has been blasted and cleared and before further work, such as drilling, on the working face commences. Permanent wooden poles or short term supports can also be used and later a support bag can be inserted between the poles to provide permanent support
Over time the temporary supports are replaced by short term supports, and then later on with permanent supports. These permanent supports include, for example, wooden support packs. Problems with wooden support packs include their cost, their weight and volume, and load capacity requirements.
An alternative to wooden support packs as permanent supports is geotextile bags. These may take the form of backfill bags, gulley packs and so forth.
Often the percolation of the bag is not in balance with the slurry mix which leads to shrinkage and later causes problems making contact with the hanging wall.
It is necessary for an underground mine support to experience a specific load before it is able to set and make contact with the hanging wall properly. This load is referred to a preload and it serves to pressurize the container sufficiently to expel excess fluid and to cause the container to be loaded to its optimum yield strength and increase the extent of contact, before the support is expected to accept full load.
A problem with existing containers used for underground mine supports is that these do not contact the hanging wall in an evenly distributed manner and experience shrinkage during setting, which also causes insufficient or no contact with the hanging wall. The uneven or insufficient contact with the hanging wall leads to unevenly distributed loads and inconsistent loads during curing or setting. This causes uneven preloading of the support, which results in the support not performing uniformly or sufficiently when under load.
In another solution non-permeable containers are used which are filled with a filler, such as a cementituous filler, that sets under pressure and over time. It is essential for such containers that the pressure be evenly distributed throughout the container to ensure even preloading and curing.
In this specification the phrase “stope design height” means the height to which a specific stope in a specific mine is specified to be developed. This is typically done by a mining engineer taking consideration of factors such as competence of the stope pillar and stope walls or stope supports, slenderness ratio of adjacent pillars, orebody dip, orebody thickness, hole depth capability of drilling machine, fragmentation characteristics of the ore, and level intervals in existing mines.
In this specification the phrase “cavity height” means the distance between a floor and a roof or between a top and a bottom of a cavity, whether temporary or permanent, in an area that requires support of a load bearing down on the roof or top of such cavity. The cavity may occur naturally, and may be man-made such as cavities under structures such as bridges, buildings, embankments and the like, and further includes cavities formed in such areas as a result of natural phenomena such as earth quakes, landslides, sinkholes and the like.
In this specification the phrase “installation height” means the mean vertical height between two vertically spaced apart surfaces, typically termed a floor and a roof, between which a support according to this invention is to be installed, and includes a stope design height and a cavity height as defined above.